1. Field of the Invention
The present invention relates to glucose sensors, and particularly to an enzyme-free cathodized gold nanoparticle graphite pencil electrode (GPE) based glucose sensor and methods for glucose detection.
2. Description of the Related Art
Glucose is an important molecule for human, plant and other living organisms. However, the presence of lower or higher concentration of dissolved glucose in blood outside of the normal range (4.4-6.6 mM) is the symptom of diseases “Diabetes mellitus”. As a result, knowing the exact glucose level in blood is crucial for diagnosis and management of Diabetes mellitus. Moreover, glucose is used in several industries such as textile, pharmaceuticals, food industries including beverages, renewable and sustainable fuel cells, and the like. Therefore, a simple, disposable, cheap, selective and sensitive glucose sensor is required for continuous glucose monitoring.
Among the common analytical methods, the electrochemical method has been widely appreciated due to its simplicity, portability, selectivity and sensitivity. Generally, electrochemical glucose sensors are classified as either (i) enzyme base glucose sensor or (ii) nonenzymatic glucose sensor. Expensive enzyme and complicated enzyme immobilization methods are required for fabrication of enzyme based electrochemical glucose sensors. Moreover, H2O2 is produced in the enzyme base glucose sensor from glucose and the produced H2O2 is oxidized on the electrode surface to generate a signal for the glucose. Practically, for oxidation of H2O2 there is typically required a potential which is high enough to oxidize interference (e.g. fructose, sucrose, ascorbic acid, dopamine uric acid etc.) in the real sample.
To overcome those problems, a plethora of nonenzymatic glucose sensors have been developed. A nonezymatic glucose sensor depends on a direct glucose oxidation signal on the electrode surface and their selectivity depends on the oxidation potential of glucose. Nanoparticles of both transition and noble metals have been used to enhance the electrocatalytic properties of a substrate electrode toward glucose oxidation. For example, gold nanowire array electrode, gold nanoparticles (Au NPs)-modified amine-functioned mesoporous silica films on glassy carbon electrode (GCE), CoOOH nanosheet-modified cobalt electrode, bimetallic Pt-M (M=Ru and Sn) NPs on carbon nanotube (CNT)-modified GCE, Pt/Ni—Co nanowires, Pd NPs on graphene oxide, Au NPs on polypyrrole nanofibers-modified GCE, copper NPs on CNT-modified GCE, Au NP-modified nitrogen-doped diamond-like carbon electrodes, AuNP/carbon nanotubes/ionic liquid nanocomposite, and Au NP-modified indium tin oxide were used to direct oxidation of glucose.
Glucose can be partially oxidized at a bulk Au electrode or a nano gold electrode at lower potential which is required to eliminate the interferences effect for detecting glucose in a real sample. However, the signal of partial oxidation of glucose in alkaline medium at Au electrode is lower than that of full oxidation at high potential. It is known that the high signal is required to obtain low detection limit in an electrochemical sensor, and that the cathodization of an Au immaterial based electrode before recording an electrochemical signal can enhance the electrochemical signal of the analyte. The reasons of limited use of Au electrode for routine analysis of glucose are high price of gold, complex preparation method of nano gold or nano gold-modified electrode and low signal at low potential.
Moreover, the graphite pencil electrode (GPE) is an attractive electrode material because it is cheap, available, possesses an easy to make renewable surface, and is relatively stable. However, graphite typically shows poor electrocatalytic properties toward many electroactive molecules. The poor electrocatalytic properties of GPE should be improved to obtain a lower detection limit in electrochemical sensors.
Thus, a cathodized gold nanoparticle graphite pencil electrode addressing the aforementioned problems is desired.